The present invention relates to a sulfur decontamination method for a three way exhaust catalytic converter of an internal combustion engine.
To meet current emission regulations, automotive vehicles must have on-board diagnostic systems to detect the malfunction of any component of the emission system, including a catalytic converter. At the same time, the exhaust system must purify the exhaust gas to reduce the concentration of certain regulated compounds. To meet the increasingly low level of exhaust emissions required, new catalytic converter formulations have been found that are more effective at accomplishing this goal. However, one drawback is that the new catalytic converter formulations are increasingly susceptible to sulfur contamination. While sulfur content in fuel is limited to 80 ppm in some states, fuel in other states can contain as much as 1000 ppm of sulfur.
Catalytic converter monitoring systems are known in which an upstream and a downstream exhaust gas oxygen sensor are compared to give an indication of catalytic degradation. If sulfur contamination occurs, these systems will diagnose the contamination and illuminate a malfunction indicator. As a result, a new catalytic converter will be required. An example of such an approach is disclosed in U.S. Pat. No. 5,357,751.
The inventors herein have recognized numerous problems with the above approaches. For example, because sulfur contamination may not be permanent, a sulfur contaminated catalytic converter would be replaced and discarded when it may be possible to decontaminate the catalytic converter and restore the exhaust purifying capability.
An object of the invention claimed herein is to provide a method to restore the exhaust purifying capability of a sulfur contaminated catalytic converter.
The above object is achieved, and problems of prior approaches overcome, by a catalytic converter decontamination method for an internal combustion engine. The method comprises the steps of: generating a catalytic converter contamination signal when catalytic converter efficiency falls below a desired level; elevating the catalytic converter temperature in response to said catalytic converter contamination signal; operating the engine in a rich condition for a first predetermined interval after said temperature elevation; and operating the engine in a lean condition for a second predetermined interval following said first predetermined interval.
By attempting to decontaminate the catalytic converter in response to degraded performance, it is possible to restore the operation of the catalytic converter if sulfur contamination was the problem. Thus, the contamination and poor performance of the catalytic converter can be remedied.
An advantage of the above aspect of the invention is that operating the engine at an elevated temperature and in a rich condition can remove sulfur contamination on the catalytic converter and increase catalytic converter performance.
Another advantage of the above aspect of the invention is that operating the engine at an elevated temperature and in a lean condition after operating at an elevated temperature and in a rich condition can further remove sulfur contamination on the catalytic converter and further increase catalytic converter performance.
Yet another advantage of the above aspect of the invention is if sulfur contamination was the cause of catalytic converter degradation, both the cost and inconvenience of a replacement system may be avoided.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.